Resistance device



Ot. 24, 17939. H. F. FRUTH 2,177,484

RESISTANCE DEVICE Filed March 25, 1955 sham-sheet 1 Oct. 24,1939. H; F, FRUTH 2,177,484

' RESISTANCE DEvIcE Filed March 2s., '1935 2 sheets-sheet 2 ATTORNEY Patented Oct.'2, 1939 UNiTEp- STATES "PATENr-foFi-icaf y v 2,177,484

Hal F. FrntlhE-rlxl'lranaNDclElianlllldlassilnor, by

Application umn es, loss, sena Nc. 12,5955.

v1 cam (ci. zar-"13) y .This invention relates to resistance deyices and more particularly to variable resistors for electric -10 Further objects are to improve the` resistor structure, the terminal and tap connections thereto, and the contacting elements therefor.

Still further objects are to improve the methods of making the resistor, including the base for the Il resistance unit, and to improve the method o applying the resistance surface thereto.

Other objects of the invention will be apparent from the following description and accompanying drawings taken in connection with the appended m claim.` The invention may be embodied in va. variable resistance device of the type commonly used in radio circuits andthe like for volume control Y purposes and in general applications to control u the amount of current owingin a circuit. In .one form, the device may comprise a ring or disc of insulating material upon the surface of which is Ian adherent coating of resistance material.y A centrally pivoted arm may be provided, carrying n a rider or contactor adapted 'to travel along said -i resistance coating in contact therewith. 'I'he invention contemplates improved methods of. making the insulating base to provide a somewhat porous adherent surface for the resistance 35 coating. It alsocontemplates a resistance coat- Y Ving of improved resistance material and an improved binder therefor whereby a uniform, highly adherent resistance surface is provided.` The` invention alsol contemplatesimproved terminal and n :ap arrangements and an improved sliding conacter.v q

The invention accordingly comprises the fea'-v tures of construction, combination .of elements,

arrangement of parts, and methods of manufac- 45Y ture referred to aboveor which will be further brought out and. exemplied in the disclosure hereinafter set forth, including the illustrations in the drawings, the scope of the invention being indicated in the appended claim.

50 f For a fuller understanding of the nature and objects of the invention as well as for speciilc fulfillment thereof, reference shouldbehad to the following detailed description taken .in connection with the accompanying drawlnss. 1,11--

u which s metal cover or cap -i9 is secured to the discs 2| Figure 1 is a face view'of the variable resistance device, with the cover therefor in section;

Figure 2 is a section on the line 2-2 of Figure l; I

Figure 3 is a back vlew'of said device; Y Y 5 yFigure 4 is a side view thereofl with the cover removed;

Figure 5 is a detail view taken on the line 5 5 of Figure 1, showing the sliding contacter;

Figure 6 is adetail sectional view taken on the line 8 6 of Figure 1, to illustrate the'terminal connection;

Figure 7 vis a face view of a'modlied form of resistance unit;

Figure 8 is a section on the linat--of Figure 7;

Figure 9 is a view of another modified form of resistance (unit with parts broken away;

Figure l0 shows a tap connecting member for the unit shown in Figure 9;

Figure 11 is a'perspective view of the resistance unit showing its structure in greater detail; c Figure 12 illustrates a method of making the insulating-backing for said resistance unit;

Figure 13 is a section through the insulating 25 backing:

Figure 14 is a section through a modied form of backing; and

Figure 15 is a section through another modified form of backing. Like reference characters indicate like parts in the several figures of the drawings.

and 22 by ears I9a and encloses the operating parts.

Super-imposed upon disc 22 of the base is a ring 22 oi.' insulating material, such as resin-impregnated fiber, havinga coating 24 of resistance material upon the outer face thereof,v the coating 24 being left of! a short sector of the insulating' ring so'that two ends to the resistance coating namnsumceumaybemrmedbysus-" pending a finely-divided resistance material, such as graphite or carbon, in a suitable liquid binder .or carrier and painting or spraying the mixture onto the surface, after which heat may be applied to dry the binder or carrier. The binder in which the finely divided resistance material is suspended may be shellac, lacquer or other resins. For example, rosin may be used, it being preferv ably deposited by the volatilization of a suitable liquid carrier or solvent. l

According to a modincation other nely-divided conductive materials may be used in place of the carbon as the resistance material. Such a material may be inely divided metal, such as niehrome, iron, silver, metallic oxide, such as copper omde, cadmium oxide, silver oxide or the. like; metallic sulfide, such as copper, cadmium or silver suliide, or the like. These materials provide superior resistance surfaces for some ap- 2() plications and may be used in suspension in liquid carriers as described for carbon. Likewise, the materials may be made of colloidal dimensions if desired to obtain a very smooth continuous surface.

Conductive terminal coatings 25 and 28 lsee Figure 6) are applied over the ends of the resistspraying metal coatings onto the ends of the resistance coating with a metal spray gun, such as is used in the Schoop process, or by spraying or painting thereon a conductive paint. Where the surface is applied by afmetal' spray gurl, the ring 22 may subsequently be placed in a press to embed the metal particles in the ring and produce a. smooth conductive surface. A' conductive paint may be made by suspending finely-divided silver oxide or silver sulide, in a carrier or vehicle,

such asgumlac or enameline "B lacquer, bronzing oil or amyl acetate. After applying the paint to the surface, the unit may be heated todrive oil the carrier and deposit the conductive com" pound in an adherent coating on the surface. A

conductive paint comprising. colloidal silver suspended in an oil may also be used.

Terminal bolts 21 and 28 pass through ring 22 ance coating to provide for a good end connec 1^ tion. The terminal portions may be applied by `and base disc 22 and are electrically connected to terminal coatings 25 and 28, respectively, by suitable conductive bushings. Terminal lugs 22 and 22 are secured by bolts 21 and 22, respectively, underneath discy 22 and project out beyond thel base to provide for external circuit connections A vist to the two ends of the resistance. surface. Bolts 21 and 28 not only serve asterminals but likewise clamp the ring 22 to base disc 22. vBolt 22 alsov has a sector 2| of an insulating material .clamped under its head to serve as a stop member for the contacter arm..

Discs 2| and 22 are clamped togetherat their- The/variable contacter stnxcture comprises a shaft'21 rotatable in bushing 22;l a contact arm 28 secured to the end of shait21 on the face side of said resistance device,` a sliding contacter mounted on theend oi' said arm and adapted to'- Aonrust slide on Iresistance surface 22, and sliding contact fingers 22 integral with said arm and adapted to slide on contact ring 22. Shaft 21 is held against axial motion by clip washer 88 fitted in an annular groove in shaft 21 adjacent therear end of bushing 22. Contact arm 28 is secured to the end of shaft 21 and insulated therefrom by a small piece of sheet insulation 2| the end of said shaft being upset to hold said piece 2| in place. Contact arm 28 and piece 2| are clamped together by a rivet pin 22. Pin 22 has a projecting portion 22 for operating a switch element which may be secured to the cover, if desired, so

that the switch actuating lever is engaged by projection 22. Arm 28 and contact ilngers 28 are of spring construction and are heldin tension by clip washer 88 so that the sliding contact portions are held in contact with their respective ring surfaces.

Sliding contacter 28 (see Figure 5) comprises a section of ve. coil spring having la plurality of turns of uniform diameter each of which is in sliding contact with the resistance surface 22 whereby a novel and highly advantageous multiple contact is made between the'arm 32 and the surface 22.

It has been found that the most desirable contact surface for a sliding contacter ls a smoothly rounded convex surface and preferably a plurality of these surfaces providingl a number of contacts over a small area of the resistor surface. Contacter 28 fulfills both of these requirements, providing a plurality of rounded contacting portions independently resiliently held against the resistor surface. Contacter 20 is iitted into a rectangular holein the end of arm 28, the hole being slightly narrower than' the diameter of the coil spring and of substantially the sainev length. Coil spring 28 is held in position by a thinsheet metal staple 22 tted over the end of arm 28 with one of its legs passing through the spring on top of the arm.

In operation, the terminal lugs 29, 28 and' are connected into an external circuit in any desired manner. By turning shaft 21 with a knob or other control means sliding contacter 28 will slide on the resistance surface 22 in a circular path, the separate turns of spring contacter 28 each bearing against surface 22 and traveling in a direction parallel to their planes. Thus the length of the resistance path, and consequently the magnitude of the'resistance in series with terminal lugs 22 and 2l or 28 and 22 may bevaried. Conductive coating 28 extends out a sumcient distance from terminal boit 21 so that contacter 28 may ride up onto it as it approaches the terminal, thereby reducing the resistance to ya negligible value. fThis enables the turning of arm 28 for a few degrees at the end of the stroke to allow for a switch to be operated by projection 22 on pip 22, if desired, without varying the resistance. The contact arm may be turned until it comes intovdirect contact with the bushing .of screw 21 connected to -lug 22, thereby reducing the resistance to substantially aero.` 0n turning the shaft in the opposite direction, however, the arm 28 is prevented from coming into contact with the terminal orterminal portion by insulating l trolled sliding contacters, like 40, riding on op" posite sides thereof. It is possible with this structure, to obtain certain desirable taper effects, and the like since the resistance coatings may be vconnected in parallel in the circuit and only one need be altered at a time.

, sheet material.

Figures 9 and 10 illustrate a means for obtaining a tap connection to the resistance unit. A band conductive material" isapplied to the surface of ring 23 over resistance surface 24 at any desired point between the ends of surface 24. Band 41 may be applied in the same manner/as terminal surfaces and 26, that is with metal Spray or paint. A metal lug A8 is then clamped to ring 23 over conductive surface 41 by projecting ears 49, integral with the lug.-

Figure 11 is a perspective view of the resistance unit used in device 20 shown in greater de- The unit comprises ring 23 of insulating tail. material, said ring being formed of laminae 50 and 5| of two different kinds. The thickness is exaggerated in the drawings for purposes of illustration. Laminae 50 may be formed of a relatively impervio'us material, for example, a synthetic resin, such as glyptal-phthalic anhydride resin, a phenolic condensation product, such as Bakelite; or a fibre impregnated with one of vthese resins; a urea resin, such as Beetleware;

cellulosic products, such as cellulose acetate, Celluloid, and the like; and other types of insulating Laminae 50 may also be formed of sheet mica built up into a laminated structure and bonded together with a suitable binder, such as a resin, a soluble silicate or the like. 'Ihe commercial laminated mica products Micanite and Micalex are suitable. Lamina 5| comprises a relatively more porous material made integral with the surface of lamina or laminae 50. Among the materials suitable for lamina 5| may be included papers of different degrees of porosity such as tissue paper, blotting paper or dexter paper, newsprint, bond paper, and manila paper; parchments, linen and straw paper and the like. The choice of material will depend upon the specific characteristics desired in the nished unit.

Resistance coating 2l and terminal surfaces 25 and 26 are applied to the porous surface of lamina 5| and since these are ordinarily applied as a paint or 'spray they will adhere perfectly to the porous surface and provide an integral unit in which there is n'o tendency for the resistance surface tofloosenor come off. This has 'a decided advantage over such units as have been previously used in which the surface has been prepared for receiving the resistance coating merely by sanding or roughening the surface or by providing a matte nish.

One method of making the insulating backing 23 is illustrated in Figure 12. A pluralityof sheets 52 of resin impregnated fiber, paper or cloth are laid in a pile and a sheet 5| of tissue paper is laid on top of the uppermost sheet and press members as shown are brought together to press the sheets into intimate contact. At the same time heat or other curing agencies are applied to the assembled sheets cementing them together. Some of y the resin material flows into the pores of tissuepaper 5| cementing this sheet to the resin impregnated backings. The resin does not impregnate sheet 5| completely, however, but passes only part of the way through the sheet, as shown in Figure 13, leaving the upper surface porous and absorbent. v

-Upon completion of the curing operation and after removal from the press, the assembly will be found to be cemented together into a unitary piece. As shown in Figure 12, the original sheets are square as that is the most readily available shape and ring 23 may be cut or stamped from the completed cemented piece. It is also possible, of course, to cut the sheets in the desired shape prior to molding. A similar procedure may be followed for the laminated mica structure. l

Figure 13 is a sectional elevation of the completed ring-23 made according to the present invention, before the application of the resistance surface. Y

Figure 14 shows a modified form of ring structure 23a in which two porous surfacing sheets 5| and 55 are used on opposite faces of the portion 50. This has a decided advantage in that the member is symmetrical and no warping will take place. Accordingly this construction of the ring is preferred for most uses. Where ring 23a is used in place of ring 23 in device 20 only one of the layers 5| and 55 is coated with the resistance material. If it is used as illustrated in Figures 7 and 8 ,both layers are coated.

Figure 15 shows a modified 'ring structure formed of a portion 50a of a non-laminated molded plastic, such as cellulose acetate, molded casein products, Beetleware and the like, for example, having porous sheets 5| and 55 molded integrally onto its two faces.

While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desiredto be limited thereby but it is intended to cover the invention broadly within the spirit and scope of ,the appended claim.

What is claimed is:

, The method of making a resistance unit which comprises forming a base of sheet synthetic resin by superposing a plurality of sheets vof material impregnated with said resin, a surface sheet containing no resin .compressing said sheets to form an integrally united sheet of material having a. surface of,low resin content, and thereafter applying a resistance lm to said low resin content surface.

HAL F. FRUTH. 

